3D image-based dosimetry for Yttrium-90 radioembolization of hepatocellular carcinoma: Impact of imaging method on absorbed dose estimates

BackgroundTo improve therapy outcome of Yttrium-90 selective internal radiation therapy (⁹⁰Y SIRT), patient-specific post-therapeutic dosimetry is required. For this purpose, various dosimetric approaches based on different available imaging data have been reported. The aim of this work was to compare post-therapeutic 3D absorbed dose images using Technetium-99m (^99mTc) MAA SPECT/CT, Yttrium-90 (⁹⁰Y) bremsstrahlung (BRS) SPECT/CT, and ⁹⁰Y PET/CT.MethodsTen SIRTs of nine patients with unresectable hepatocellular carcinoma (HCC) were investigated. The ^99mTc SPECT/CT data, obtained from ^99mTc-MAA-based treatment simulation prior to ⁹⁰Y SIRT, were scaled with the administered ⁹⁰Y therapy activity. 3D absorbed dose images were generated by dose kernel convolution with scaled ^99mTc/⁹⁰Y SPECT/CT, ⁹⁰Y BRS SPECT/CT, and ⁹⁰Y PET/CT data of each patient. Absorbed dose estimates in tumor and healthy liver tissue obtained using the two SPECT/CT methods were compared against ⁹⁰Y PET/CT.ResultsThe percentage deviation of tumor absorbed dose estimates from ⁹⁰Y PET/CT values was on average −2 ± 18% for scaled ^99mTc/⁹⁰Y SPECT/CT, whereas estimates from ⁹⁰Y BRS SPECT/CT differed on average by −50 ± 13%. For healthy liver absorbed dose estimates, all three imaging methods revealed comparable values.ConclusionThe quantification capabilities of the imaging data influence ⁹⁰Y SIRT tumor dosimetry, while healthy liver absorbed dose values were comparable for all investigated imaging data. When no ⁹⁰Y PET/CT image data are available, the proposed scaled ^99mTc/⁹⁰Y SPECT/CT dosimetry method was found to be more appropriate for HCC tumor dosimetry than ⁹⁰Y BRS SPECT/CT based dosimetry.     

Comparison of 90Y SIRT predicted and delivered absorbed doses using a PSF conversion method

PurposeThe aims of this study were to develop and apply a method to correct for the differences in partial volume effects of pre-therapy Technetium-99 m (^99mTc)-MAA SPECT and post-therapy Yttrium-90 (⁹⁰Y) bremsstrahlung SPECT imaging in selective internal radiation therapy, and to use this method to improve quantitative comparison of predicted and delivered ⁹⁰Y absorbed doses.MethodsThe spatial resolution of ^99mTc SPECT data was converted to that of ⁹⁰Y SPECT data using a function calculated from ^99mTc and ⁹⁰Y point spread functions. This resolution conversion method (RCM) was first applied to ^99mTc and ⁹⁰Y SPECT phantom data to validate the method, and then to clinical data to assess the power of ^99mTc SPECT imaging to predict the therapeutic absorbed dose.ResultsThe maximum difference between absorbed doses to phantom spheres was 178%. This was reduced to 27% after the RCM was applied.The clinical data demonstrated differences within 38% for mean absorbed doses delivered to the normal liver, which were reduced to 20% after application of the RCM. Analysis of clinical data showed that therapeutic absorbed doses delivered to tumours greater than 100 cm³ were predicted to within 52%, although there were differences of up to 210% for smaller tumours, even after the RCM was applied.ConclusionsThe RCM was successfully verified using phantom data. Analysis of the clinical data established that the ^99mTc pre-therapy imaging was predictive of the ⁹⁰Y absorbed dose to the normal liver to within 20%, but had poor predictability for tumours smaller than 100 cm³.     

Calculation of tumour and normal tissue biological effective dose in 90Y liver radioembolization with different dosimetric methods

PurposeRadioembolization with ⁹⁰Y microspheres is an effective treatment for unresectable liver tumours. Two types of microspheres are available: resin (SIR-Spheres®) and glass (Theraspheres®). The aim of this study is to compare biological effective dose (BED) values obtained with three different dosimetric methods.Methods29 HCC patients were included in this study: 15 were treated with resin(mean injected activity 1.5 GBq, range 0.8–2.7 GBq) and 14 with glass microspheres (2.6 GBq, range 1.3–4.1 GBq). Average doses to tumours and normal liver tissues were calculated with AAPM, multi-compartmental MIRD and Voxel-based methods and consequently the BED values were obtained. Planar images were used for the AAPM method: ^99mTc-MAA SPECT-CT attenuation and scatter corrected images (resin) and ⁹⁹m Tc-MAA SPECT attenuation corrected (glass) were employed for the other two methods.ResultsRegardless of type of microspheres, both for tumours and normal liver tissues, no significant statistical differences were found between MIRD and Voxel for both doses and BED values. Conversely AAPM gave discordant results with respect to the other two methods (Mann-Whitney p-values ⩽ 0.01). For resin spheres the calculated tumour-to-normal tissue ratios on planar images were on average 14 times greater than those obtained on SPECT-CT images, while they were 4 times greater on glass. A linear correlation was observed between MIRD and Voxel BEDs.ConclusionsThe AAPM method appears to be less precise for absorbed dose and BED estimation, while MIRD and voxel based dosimetry are more confident each other.     

Generation of clinical 177Lu SPECT/CT images based on Monte Carlo simulation with GATE

PurposePatient-specific dosimetry in MRT relies on quantitative imaging, pharmacokinetic assessment and absorbed dose calculation. The DosiTest project was initiated to evaluate the uncertainties associated with each step of the clinical dosimetry workflow through a virtual multicentric clinical trial. This work presents the generation of simulated clinical SPECT datasets based on GATE Monte Carlo modelling with its corresponding experimental CT image, which can subsequently be processed by commercial image workstations.MethodsThis study considers a therapy cycle of 6.85 GBq ¹⁷⁷Lu-labelled DOTATATE derived from an IAEA-Coordinated Research Project (E23005) on “Dosimetry in Radiopharmaceutical therapy for personalised patient treatment”. Patient images were acquired on a GE Infinia-Hawkeye 4 gamma camera using a medium energy (ME) collimator. Simulated SPECT projections were generated based on experimental time points and validated against experimental SPECT projections using flattened profiles and gamma index. The simulated projections were then incorporated into the patient SPECT/CT DICOM envelopes for processing and their reconstruction within a commercial image workstation.ResultsGamma index passing rate (2% − 1 pixel criteria) between 95 and 98% and average gamma between 0.28 and 0.35 among different time points revealed high similarity between simulated and experimental images. Image reconstruction of the simulated projections was successful on HERMES and Xeleris workstations, a major step forward for the initiation of a multicentric virtual clinical dosimetry trial based on simulated SPECT/CT images.ConclusionsRealistic ¹⁷⁷Lu patient SPECT projections were generated in GATE. These modelled datasets will be circulated to different clinical departments to perform dosimetry in order to assess the uncertainties in the entire dosimetric chain.     

Faisabilité et intérêt d’un nouvel algorithme de reconstruction des images TEP-18FDG (AW OSEM DR) pour la délimitation des volumes cibles en radiothérapie. À propos d’un cas de néoplasie ORL

ObjectiveWe compared two reconstruction methods for 18fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography (PET) images with “attenuation weighted ordered subset expectation maximization” using either the manufacturer-provided (AW-OSEM) or a “Detector response” (AW-OSEM DR) tomographic operator. We looked at the feasibility of using the latter reconstruction for radiotherapy target volumes definition in cancers of the superior aero-digestive tract (VADS). In this preliminary study, we first assessed the spatial resolution of images obtained with AW-OSEM and AW-OSEM DR on a Biograph™ 6, and secondly target volumes of radiotherapy “Gross Tumor Volume” (GTV), “Clinical Target Volume” (CTV) and “Planning Target Volume” (PTV) obtained with each of these reconstruction methods.Material and methodsThe spatial resolution was measured on a test object containing 4 radioactive point sources. Furthermore, radiotherapy target volumes have been defined with the software Eclipse™ on injected scanner (CT IV) and PET/CT (PET AW-OSEM and PET AW-OSEM DR) images.ResultsSpatial resolution was improved with AW-OSEM DR algorithm reconstruction compared to images obtained with AW-OSEM reconstruction (from 7.5 mm down to 5.4 mm for the highest reduction). GTV from AW-OSEM DR reconstruction with 42 and 50% of the “Standard uptake value maximum” (SUVmax) semi-automatic threshold (1.2 and 0.7 cm³ respectively) were lower than those obtained with AW-OSEM (3.6 and 2.2 cm³ respectively). They were also lower than GTV defined with CT IV (5.5 cm³). It was the same for CTV and PTV.ConclusionThis study showed that AW-OSEM DR reconstruction method allows less impaired spatial resolution than AW-OSEM. In the case of radiotherapy target volumes delineation, AW-OSEM DR may decrease the GTV, CTV and PTV and therefore the risk of side effects associated with organs at risk.     

Liver Selective Internal Radiation Therapy with 90Y resin microspheres: Comparison between pre-treatment activity calculation methods

Different methods to calculate ⁹⁰Y resin microspheres activity for Selective Internal Radiation Therapy (SIRT) were compared. Such comparison is not yet available and is needed in clinical practice to optimize patient specific treatment planning.32 ^99mTc-macroagregates (MAA) evaluations were performed, followed by 26 treatments. Four methods to calculate ⁹⁰Y-activity were applied retrospectively: three based on Body Surface Area and one based on MIRD formalism, partition model (PM). Relationships between calculated activities, lung breakthrough (LB), the activity concentration ratio between lesions and healthy liver (T/N) and tumour involvement were investigated, where lobar and whole liver treatments were analysed separately.Without attenuation correction, overestimation of LB was 65%. In any case, the estimated lungs' doses remained below 30 Gy. Thus, the maximal injectable activity (MIA) is not limited by lungs' irradiation. Moreover, LB was not significantly related to T/N, neither to tumour involvement nor radiochemical purity (RP).Differences in calculated activity with the four methods were extremely large, in particular they were greater between BSA-based and PM activities for lobar treatments (from −85% to 417%) compared to whole liver treatments (from −49% to 61%). Two values of T/N ratio were identified as thresholds: for BSA-based methods, healthy liver doses are much higher than 30 Gy when T/N < 3; for PM, tumour doses are higher than 120 Gy when T/N > 4.As PM accounts for uptake ratio between normal and tumour liver, this method should be employed over BSA-based methods.     

Distributions of perfusion and lung water

We investigated the feasibility of using ¹²³I-iodoantipyrine (¹²³I-IAP) and ^99mTc-labeled macroaggregated albumin (^99mTc-MAA) to describe and compare the distributions of perfusion and water content in lung injuries. These radiopharmaceuticals were administered to 9 rabbits, 5 control and 4 with lung injuries. Isolated lungs were imaged by a scintillation γ camera. The distribution of ¹²³I-IAP outlined the entire lung mass whereas perfusion defect in the distribution of ^99mTc-MAA was seen clearly in the case of severe lung injury.     

Apport de la scintigraphie rénale dynamique au 99mTc-DTPA avec épreuve au furosémide dans l’exploration du syndrome de la jonction pyélo-urétérale a minima. À propos de 17 cas

IntroductionThe renal scintigraphy using ^99mTc-DTPA with furosemid test constitutes a noninvasive and functional method that is of appreciable interest in the exploration of the upper urinary tract and in the evaluation of the separate renal function. It distinguishes the functional character of dilation from organic obstruction needing surgery or endoscopic treatment.Material and methodsWe report, through this work, the observations of 17 patients with a low grade ureteropelvic junction syndrome detect by intravenous urography (IVU). ^99mTc-DTPA renal scintigraphy with furosemid test was carried out among all our patients by means of a gamma-camera with large field equipped with a low energy high-resolution parallel collimator. The evaluation of images obtained consisted of analysis of ureteropelvic permeability taking into account the semiquantitative parameters of time-activity curve or isotopic nephrogram (IN) obtained after digital reconstruction of sequential images.ResultsOn the 17 studied cases, the sex-ratio was equal to 1.83; the average age was 18.92 years with extremes spanning from 4 years to 70 years. Renal scintigraphy categorised four patients groups. Group I: two patients (11.76%) with normal aspect of IN; group II; seven patients (41.17% of cases) with functional dilation; groupe III: five patients (29.41%) with organic obstruction and a group IV: three patients (17.64%) with intermediate response.Discussion^99mTc-DTPA renal scintigraphy with furosemid test allowed, through our study, to obviate the limits of IVU and manometric explorations to distinguish functional dilation of organic obstruction. It permits the improvement of treatment with a favourable dosimetry.     

A new cone-beam computed tomography dosimetry method providing optimal measurement positions: A Monte Carlo study

PurposeThe conventional weighted computed tomography dose index (CTDI_w) may not be suitable for cone-beam computed tomography (CBCT) dosimetry because a cross-sectional dose distribution is angularly inhomogeneous owing to partial angle irradiations. This study was conducted to develop a new dose metric (f(0)^CB_w) for CBCT dosimetry to determine a more accurate average dose in the central cross-sectional plane of a cylindrical phantom using Monte Carlo simulations.MethodsFirst, cross-sectional dose distributions of cylindrical polymethyl methacrylate phantoms over a wide range of phantom diameters (8–40 cm) were calculated for various CBCT scan protocols. Then, by obtaining linear least-squares fits of the full datasets of the cross-sectional dose distributions, the optimal radial positions, which represented measurement positions for the average phantom dose, were determined. Finally, the f(0)^CB_w method was developed by averaging point doses at the optimal radial positions of the phantoms. To demonstrate its validity, the relative differences between the average doses and each dose index value were estimated for the devised f(0)^CB_w, conventional CTDI_w, and Haba’s CTDI_w methods, respectively.ResultsThe relative differences between the average doses and each dose index value were within 4.1%, 16.7%, and 11.9% for the devised, conventional CTDI_w, and Haba’s CTDI_w methods, respectively.ConclusionsThe devised f(0)^CB_w value was calculated by averaging four “point doses” at 90° intervals and the optimal radial positions of the cylindrical phantom. The devised method can estimate the average dose more accurately than the previously developed CTDI_w methods for CBCT dosimetry.     

The effect of tumour geometry on the quantification accuracy of planar 123I phantom images

IntroductionAccurate activity quantification is applied in radiation dosimetry. Planar images are important for quantification of whole-body images, enabling assessment of biodistribution from radionuclide administrations. We evaluated the effect of tumour geometry on quantification accuracy of ¹²³I planar phantom studies, including various tumour sizes, tumour-liver distances and two tumour-background ratios.Methods and materialsAn in-house manufactured abdominal phantom was equipped with a liver, different size cylindrical tumours, and a rod for tumour-liver distance variation. The geometric mean method with scatter and attenuation corrections was used for image processing. Scatter and attenuation corrections were made using the triple energy window scatter correction technique and a printed transmission sheet source, respectively. Region definitions for tumour activity distribution compensated for the partial volume effect (PVE). Activity measured in the dose calibrator served as reference for determining quantification accuracy.ResultsThe smallest tumour had the largest percentage deviation with an average activity underestimation of 34.6 ± 1.2%. Activity values for the largest tumour were overestimated by 3.1 ± 3.0%. PVE compensation improved quantification accuracy for all tumour sizes yielding accuracies of <12.4%. Scatter contribution to the tumours from the liver had minimal effect on quantification accuracy at tumour-liver distances >3 cm. With PVE compensation, increased tumour-background ratio resulted in a percentage increase of up to 26.3%.ConclusionWhen applying relevant corrections for scatter, attenuation and PVE without background activity, quantification accuracy of <13% was obtained. We demonstrated the successful implementation of a practical technique to obtain quantitative information from ¹²³I planar images.     

Error detection during VMAT delivery using EPID-based 3D transit dosimetry

PurposeTo investigate the effectiveness of an EPID-based 3D transit dosimetry system in detecting deliberately introduced errors during VMAT delivery.MethodsAn Alderson phantom was irradiated using four VMAT treatment plans (one prostate, two head-and-neck and one lung case) in which delivery, thickness and setup errors were introduced. EPID measurements were performed to reconstruct 3D dose distributions of “error” plans, which were compared with “no-error” plans using the mean gamma (γ_mean), near-maximum gamma (γ_1%) and the difference in isocenter dose (ΔD_isoc) as metrics.ResultsOut of a total of 42 serious errors, the number of errors detected was 33 (79%), and 27 out of 30 (90%) if setup errors are not included. The system was able to pick up errors of 5 mm movement of a leaf bank, a wrong collimator rotation angle and a wrong photon beam energy. A change in phantom thickness of 1 cm was detected for all cases, while only for the head-and-neck plans a 2 cm horizontal and vertical shift of the phantom were alerted. A single leaf error of 5 mm could be detected for the lung plan only.ConclusionAlthough performed for a limited number of cases and error types, this study shows that EPID-based 3D transit dosimetry is able to detect a number of serious errors in dose delivery, leaf bank position and patient thickness during VMAT delivery. Errors in patient setup and single leaf position can only be detected in specific cases.     

Hypoxia and Exercise Increase the Transpulmonary Passage of 99mTc-Labeled Albumin Particles in Humans

Intrapulmonary arteriovenous anastomoses (IPAVs) are large diameter connections that allow blood to bypass the lung capillaries and may provide a route for right-to-left embolus transmission. These anastomoses are recruited by exercise and catecholamines and hypoxia. Yet, whether IPAVs are recruited via direct, oxygen sensitive regulatory mechanisms or indirect effects secondary to redistribution pulmonary blood flow is unknown. Here, we hypothesized that the addition of exercise to hypoxic gas breathing, which increases cardiac output, would augment IPAVs recruitment in healthy humans. To test this hypothesis, we measured the transpulmonary passage of ^99mTc-macroaggregated albumin particles (^99mTc-MAA) in seven healthy volunteers, at rest and with exercise at 85% of volitional max, with normoxic (FIO₂ = 0.21) and hypoxic (FIO₂ = 0.10) gas breathing. We found increased ^99mTc-MAA passage in both exercise conditions and resting hypoxia. However, contrary to our hypothesis, we found the greatest ^99mTc-MAA passage with resting hypoxia. As an additional, secondary endpoint, we also noted that the transpulmonary passage of ^99mTc-MAA was well-correlated with the alveolar-arterial oxygen difference (A-aDO₂) during exercise. While increased cardiac output has been proposed as an important modulator of IPAVs recruitment, we provide evidence that the modulation of blood flow through these pathways is more complex and that increasing cardiac output does not necessarily increase IPAVs recruitment. As we discuss, our data suggest that the resistance downstream of IPAVs is an important determinant of their perfusion.     

99mTc标记BmK CT及其胶质瘤荷瘤裸鼠的SPECT成像研究

目的:通过放射性核素~(99m)Tc标记BmK CT多肽制备靶向胶质瘤的显像剂,探讨~(99m)?Tc-BmK CT用于胶质瘤显像的可行性。方法:采用BmK CT多肽游离的氨基与DTPA酸酐反应得到BmK CT-DTPA,经99m Tc标记后通过柱层析分离纯化制备~(99m)?Tc-BmK CT。测定标记物在PBS溶液和血清中不同时间点放射性化学纯度,评价BmK CT-~(99m)?Tc体外稳定性。新西兰白兔耳缘静脉注射~(99m)Tc-BmK CT进行SPECT显像,观察不同时间点体内的放射性分布。皮下胶质瘤裸鼠经尾静脉注射~(99m)Tc-BmK CT,观察不同时间点肿瘤的摄取情况;注射后4 h处死裸鼠,分离肿瘤和主要器官进行离体SPECT显像,并用勾画感兴趣区法分析相对放射性计数。结果:~(99m)Tc标记BmK CT多肽标记率大于80%,经柱层析分离纯化后放射性化学纯度大于99%。标记物在PBS和血清稳定性良好,6 h内放射性化学纯度均大于95%,12 h内放射性化学纯度大于90%。正常白兔SPECT显像表明~(99m)Tc-BmK CT主要浓聚在肝脏、脾脏和肾脏,软组织持续显影微弱,甲状腺区及胃肠未见核素浓聚;显像剂主要通过泌尿系统排泄,24 h肾脏与肝脏显影接近。胶质瘤裸鼠SPECT显像表明,注射后4 h肿瘤显像清楚,ROI分析结果显示肿瘤/肌肉比4.26±0.25,标记物在肿瘤内代谢缓慢,8 h肿瘤部位仍有较高摄取。结论:本研究成功制备了~(99m)Tc标记BmK CT多肽,标记物主要被肝、脾和肾摄取,经泌尿系统排泄;~(99m)Tc-BmK CT能够在皮下胶质瘤中浓聚,注射后4 h肿瘤显影清晰,瘤内代谢缓慢,有潜力成为一种新型胶质瘤分子探针。     

Sensitization of Chemo-Resistant Human Chronic Myeloid Leukemia Stem-Like Cells to Hsp90 Inhibitor by SIRT1 Inhibition

Development of effective therapeutic strategies to eliminate cancer stem-like cells (CSCs), which play a major role in drug resistance and disease recurrence, is critical to improve cancer treatment outcomes. The current investigation was undertaken to examine the effectiveness of the combination treatment of Hsp90 inhibitor and SIRT1 inhibitor in inhibiting the growth of chemo-resistant stem-like cells isolated from human chronic myeloid leukemia K562 cells. Inhibition of SIRT1 by use of SIRT1 siRNA or SIRT1 inhibitors (amurensin G and EX527) effectively potentiated sensitivity of Hsp90 inhibitors (17-AAG and AUY922) in CD44^high K562 stem-like cells expressing high levels of CSC-related molecules including Oct4, CD34, β-catenin, c-Myc, mutant p53 (mut p53), BCRP and P-glycoprotein (P-gp) as well as CD44. SIRT1 depletion caused significant down-regulation of heat shock factor 1 (HSF1)/heat shock proteins (Hsps) as well as these CSC-related molecules, which led to the sensitization of CD44^high K562 cells to Hsp90 inhibitor by SIRT1 inhibitor. Moreover, 17-AAG-mediated activation of HSF1/Hsps and P-gp-mediated efflux, major causes of Hsp90 inhibitor resistance, was suppressed by SIRT1 inhibitor in K562-CD44^high cells. Our data suggest that combined treatment with Hsp90 inhibitor and SIRT1 inhibitor could be an effective therapeutic approach to target CSCs that are resistant to current therapies.     

SIRT2 suppresses expression of inflammatory factors via Hsp90‐glucocorticoid receptor signalling

SIRT2 is a NAD⁺‐dependent deacetylase that deacetylates a diverse array of protein substrates and is involved in many cellular processes, including regulation of inflammation. However, its precise role in the inflammatory process has not completely been elucidated. Here, we identify heat‐shock protein 90α (Hsp90α) as novel substrate of SIRT2. Functional investigation suggests that Hsp90 is deacetylated by SIRT2, such that overexpression and knock‐down of SIRT2 altered the acetylation level of Hsp90. This subsequently resulted in disassociation of Hsp90 with glucocorticoid receptor (GR), and translocation of GR to the nucleus. This observation was further confirmed by glucocorticoid response element (GRE)‐driven reporter assay. Nuclear translocation of GR induced by SIRT2 overexpression repressed the expression of inflammatory cytokines, which were even more prominent under lipopolysaccharide (LPS) stimulation. Conversely, SIRT2 knock‐down resulted in the up‐regulation of cytokine expression. Mutation analysis indicated that deacetylation of Hsp90 at K294 is critical for SIRT2‐mediated regulation of cytokine expression. These data suggest that SIRT2 reduces the extent of LPS‐induced inflammation by suppressing the expression of inflammatory factors via SIRT2‐Hsp90‐GR axis.     

Simplified patient-specific renal dosimetry in 177Lu therapy: a proof of concept

PurposeThe aim of this proof-of-concept study is to propose a simplified personalized kidney dosimetry procedure in ¹⁷⁷Lu peptide receptor radionuclide therapy (PRRT) for neuroendocrine tumors and metastatic prostate cancer. It relies on a single quantitative SPECT/CT acquisition and multiple radiometric measurements executed with a collimated external probe, properly directed on kidneys.MethodsWe conducted a phantom study involving external count-rate measurements in an abdominal phantom setup filled with activity concentrations of ^99mTc, reproducing patient-relevant organ effective half-lives occurring in ¹⁷⁷Lu PRRT. GATE Monte Carlo (MC) simulations of the experiment, using ^99mTc and ¹⁷⁷Lu as sources, were performed. Furthermore, we tested this method via MC on a clinical case of ¹⁷⁷Lu-DOTATATE PRRT with SPECT/CT images at three time points (2, 20 and 70 hrs), comparing a simplified kidney dosimetry, employing a single SPECT/CT and probe measurements at three time points, with the complete MC dosimetry.ResultsThe experimentally estimated kidney half-life with background subtraction applied was compatible within 3% with the expected value. The MC simulations of the phantom study, both with ^99mTc and ¹⁷⁷Lu, confirmed a similar level of accuracy. Concerning the clinical case, the simplified dosimetric method led to a kidney dose estimation compatible with the complete MC dosimetry within 6%, 12% and 2%, using respectively the SPECT/CT at 2, 20 and 70 hrs.ConclusionsThe proposed simplified procedure provided a satisfactory accuracy and would reduce the imaging required to derive the kidney absorbed dose to a unique quantitative SPECT/CT, with consequent benefits in terms of clinic workflows and patient comfort.     

Evaluation of two-dimensional electronic portal imaging device using integrated images during volumetric modulated arc therapy for prostate cancer

BackgroundThe aim of the study was to evaluate analysis criteria for the identification of the presence of rectal gas during volumetric modulated arc therapy (VMAT) for prostate cancer patients by using electronic portal imaging device (EPID)-based in vivo dosimetry (IVD).Materials and methodsAll measurements were performed by determining the cumulative EPID images in an integrated acquisition mode and analyzed using PerFRACTION commercial software. Systematic setup errors were simulated by moving the anthropomorphic phantom in each translational and rotational direction. The inhomogeneity regions were also simulated by the I’mRT phantom attached to the Quasar phantom. The presence of small and large air cavities (12 and 48 cm³) was controlled by moving the Quasar phantom in several timings during VMAT. Sixteen prostate cancer patients received EPID-based IVD during VMAT.ResultsIn the phantom study, no systematic setup error was detected in the range that can happen in clinical (< 5-mm and < 3 degree). The pass rate of 2% dose difference (DD2%) in small and large air cavities was 98.74% and 79.05%, respectively, in the appearance of the air cavity after irradiation three quarter times. In the clinical study, some fractions caused a sharp decline in the DD2% pass rate. The proportion for DD2% < 90% was 13.4% of all fractions. Rectal gas was confirmed in 11.0% of fractions by acquiring kilo-voltage X-ray images after the treatment.ConclusionsOur results suggest that analysis criteria of 2% dose difference in EPID-based IVD was a suitable method for identification of rectal gas during VMAT for prostate cancer patients.     

188Re image performance assessment using small animal multi-pinhole SPECT/PET/CT system

PurposeThe goal of this study was to investigate the performance of a pre-clinical SPECT/PET/CT system for ¹⁸⁸Re imaging.MethodsPhantom experiments were performed aiming to assess the characteristics of two multi-pinhole collimators: ultra-high resolution collimator (UHRC) and high-energy ultra high resolution collimator (HE-URHC) for imaging ¹⁸⁸Re. The spatial resolution, image contrast and contrast-to-noise ratio (CNR) were investigated using micro-Jaszczak phantoms. Additionally, the quantification accuracy of ¹⁸⁸Re images was evaluated using two custom-designed phantoms. The ¹⁸⁸Re images were compared to those obtained with ^99mTc (gold standard); the acquired energy spectra were analyzed and Monte-Carlo simulations of the UHRC were performed. To verify our findings, a C57BL/6-mouse was injected with ¹⁸⁸Re-microspheres and scanned with both collimators.ResultsThe spatial resolution achieved in ¹⁸⁸Re images was comparable to that of ^99mTc. Acquisitions using HE-UHRC yielded ¹⁸⁸Re images with higher contrast and CNR than UHRC. Studies of quantitative accuracy of ¹⁸⁸Re images resulted in <10% errors for both collimators when the activity was calculated within a small VOI around the object of interest. Similar quantification accuracy was achieved for ^99mTc. However, ¹⁸⁸Re images showed much higher levels of noise in the background. Monte-Carlo simulations showed that ¹⁸⁸Re imaging with UHRC is severely affected by down-scattered photons from high-energy emissions. The mouse images showed similar biodistribution of ¹⁸⁸Re-microspheres for both collimators.ConclusionsVECTor/CT provided ¹⁸⁸Re images quantitatively accurate and with quality comparable to ^99mTc. However, due to large penetration of UHRC by high-energy photons, the use of the HE-UHRC for imaging ¹⁸⁸Re in VECTor/CT is recommended.     

Quantization accuracy of short-duration respiratory-gated PET/CT acquisitions

PurposePET/CT acquisitions are affected by physiological motion, which lowers the quantization accuracy. Respiratory-gated PET/CT methods require a long acquisition time, which may not be compatible with the clinical schedule. The objective of the present study was to assess the quantization accuracy of short-duration, respiratory-gated PET acquisitions and processing with the “CT-based” methodology developed in our laboratory.MethodsQuantization accuracy was first assessed in a phantom study. A standard (“Ungated”) PET/CT acquisition was followed by a 10-minute list-mode acquisition with simultaneous respiratory signal recording and a short breath-hold CT scan (BH-CT). These acquisitions were repeated 10 times. For the CT-based images, we reconstructed (i) 10 full-duration (FD-CT-based) volumes that took account of all events recorded in the position defined by BH-CT and (ii) 10 short-duration (SD-CT-based) volumes based on only 30 seconds of selected events. Using these volumes, we performed a bias–variance analysis to assess the effects of respiration-motion reduction and the counting statistics on the quantization accuracy. We also applied Ungated, FD- and SD-CT-based methods to 16 patients (21 pulmonary lesions) and measured the maximum standardized uptake (SUVmax) values.ResultsThe bias values were 71%, 40% and 44% for Ungated, FD- and SD-CT-based images, respectively. In the clinical study, there was a statistically significant difference in SUVmax between Ungated images and both the CT-Based images (p < 0.02) but not between the FD-CT-Based and SD-CT-Based images (p = 0.42).ConclusionOur findings demonstrated that the additional acquisition time required by the CT-based method can be reduced without altering quantitative accuracy.     

Évaluation de la cinétique globale et segmentaire du ventricule gauche chez les patients connus ou suspects de cardiopathie ischémique : comparaison des données apportées en scintigraphie de perfusion myocardique et en tomoventriculographie isotopique

Background and aimsThe analysis of the left ventricular contractile function plays a major role in the diagnosis and management of patients with cardiopathies. The aim of our study was to compare gated blood pool SPECT and myocardial perfusion scintigraphy for the assessment of the left ventricular wall contractility at the global and the segmental scales.Material and methodsThe data of 23 ^99mTc-Tetrofosmin perfusion scintigraphies, and 50 ²⁰¹Thallium perfusion scintigraphies were compared to those of gated blood pool SPECT performed at close interval.ResultsThe correlations were good (r = 0.81 to 0.94) concerning the global parameters (left ventricular ejection fraction, end-diastolic and end-systolic volumes) in the two groups. Quite good correlations were also found at the segmental scale (r = 0.49 to 0.62), between the segmental ejection fraction calculated in gated blood pool SPECT and the wall thickening or the wall motion estimated in perfusion scintigraphy. These correlations were significantly lower in the “²⁰¹Thallium perfusion scintigraphy” group than in the “^99mTc-Tetrofosmin perfusion scintigraphy” group, especially for hypokinetic segments.ConclusionAlthough they use very different approaches, GBPS and MPS give data about global and segmental left ventricular wall contraction that are well correlated, but not strictly interchangeable.